National security advisor Michael Flynn resigned Monday, citing "incomplete information" that he provided to top White House officials about his dealings with the Russian ambassador.

"Unfortunately, because of the fast pace of events, I inadvertently briefed the vice-president elect and others with incomplete information regarding my phone calls with the Russian Ambassador," Flynn wrote in a public statement. "I have sincerely apologized to the President and the Vice President, and they have accepted my apology."

Trump immediately named Lt. General Joseph Keith Kellogg, Jr., as acting national security adviser, the White House reported.

Former acting attorney general Sally Yates warned the White House that Flynn was misleading about the interactions with the ambassador, an official told USA TODAY.

The official, who is not authorized to comment publicly on the matter, said Yates’ communication to the White House was prompted by assertions from top Trump officials, including Vice President Pence, that Flynn had not discussed sanctions imposed by the Obama administration for Russia’s meddling in the 2016 election.

The Washington Post first reported the development earlier Monday.

Yates, a holdover from the Obama administration, was abruptly dismissed by the White House earlier this month after directing Justice lawyers not to defend the new administration’s travel ban against seven Muslim-majority countries.

Former director of national intelligence James Clapper and former CIA director John Brennan concurred with Yates, the Post reported.

In the message, Yates and the other official named Vice President Mike Pence as one of the officials that Flynn misled about his communication with Russian Ambassador Sergey Kislyak shortly after sanctions were announced in the final days of the Obama administration.

White House Press Secretary Sean Spicer said in a statement released Monday night that President Trump is evaluating the situation with Flynn.

"The president is evaluating the situation," according to the statement. "He's speaking to the vice president relative to the conversation the vice president had with Gen. Flynn, and also speaking to various other people about what he considers the single most important subject there is: our national security."

On Feb. 8, Flynn categorically denied to the Post that he discussed sanctions with Kislyak, but the next day, he changed his testimony, telling the news organization that he "couldn't be certain that the topic never came up," according to the Post.

U.S. intelligence reports during the White House campaign last year show that Kislyak and Flynn were in touch, the Post reported. Kislyak confirmed he and Flynn communicated but he declined to discuss the topic, according to the Post.

Trump counselor Kellyanne Conway told MSNBC that Trump has "full confidence" in Flynn. But one official told CNN that Flynn's future could be shaky given the development. "There's a lot of unhappiness over this," the official told the news organization.

Yates was dismissed by President Trump on Jan. 30 after instructing the Department of Justice not to defend his travel ban in court.

Late Monday night, Rep. Mike Coffman, R-Colo.., weighed in on the controversy, saying Flynn should resign from his position if the reports are deemed true.

“As national security advisor, Michael Flynn is responsible to the President, the Vice President, and the American people,” Coffman said on his official Twitter account. "It is his duty to be fully transparent and forthright in his actions — anything less is unacceptable. If in fact he purposely misled the President, he should step down immediately.”